This seems to be quite critical bug:
1. select data on a table
2. select row by checkbox
3. click delete
4. dialog "are you sure (1)?" appears
5. click cancel
6. row is deleted anyway
Can reproduce anytime. I am on Google Chrome v16.
I just found out that it happens only sometimes.
I can cofirm this on my second computer at work.
Probably a bug in Google Chrome
Maybe this happened because a weird AJAX behavior in Chrome and shouldn't appear in Adminer 3.4.0 which removed the AJAXification.